64 Dart GT Slant 6 Electric Fan Conversion

I have to admit, that fan controller has got to be the best.
It's the easiest one to install with that kind of functionality. And it's made in the USA. But it's not perfect, none are in my experience.

There are some caveats. That controller doesn't like to get too hot (most don't). So you got to mount it where there is airflow. And mine took a long time to arrive. I would talk to the guy and get an ETA before ordering.

There is Dakota Digital which can use your stock temp sensor. But it's a complicated install and I can't remember if it ramps or not. No EFI and having a smaller fan with a short run to the battery, ramping may not be required.

The FK-45 uses a plug-in sensor to the radiator fins. I don't care for those, but this sensor is the best of it's ilk.

There are other newer efan controller offerings out there from the usual vendors that you should look at too. I can't use any of them though because the fans I use draw too much current. Big electric fans draw an obnoxious amount of current at startup.